In organic electroluminescent display devices or semiconductor devices, a thin film pattern may be formed on a substrate by using a shadow mask having desired patterns. More particularly, the shadow mask and the substrate are disposed over a source such that the shadow mask is interposed between the substrate and the source. Then, the source is evaporated and deposited on the substrate through the shadow mask.
In general, a shadow mask is attached to a substrate holder with a substrate in a chamber. The shadow mask and the substrate may be fixed to the substrate holder by a mechanical fixing method or a magnetic fixing method. In the mechanical fixing method, sides of the substrate holder, the shadow mask and the substrate may be mechanically fixed using pins or clips. In the magnetic fixing method, the shadow mask is formed of a magnetic substance, and the substrate and the shadow mask may be magnetically fixed to the substrate holder by permanent magnets or electromagnets.
In the magnetic fixing method, the shadow mask may be magnetized, and adjacent patterns of the shadow mask are contacted to each other due to the magnetization, causing undesirable patterns on the substrate.
FIGS. 1 and 2 are views illustrating an apparatus for forming a thin film using a magnetic shadow mask according to the related art.
As shown in FIG. 1, a shadow mask 102 is disposed over a mask holder 103 in a process chamber 101. A substrate 105 is disposed over a substrate holder 104, which is set up over shadow mask 102 in the process chamber 101.
The shadow mask 102 is formed of an invar, which is an alloy of ferromagnetic iron and nickel and has a relatively low coefficient of thermal expansion. The shadow mask 102 is perforated corresponding to patterns.
Two cross patterns (not shown) are formed on each of the substrate 105 and the shadow mask 102. While the cross patterns are monitored through charge-coupled device (CCD) cameras 106, the substrate 105 moves in an x, y, z or θ direction according to images from the CCD cameras 106. Therefore, the substrate 105 and the shadow mask 102 are aligned with each other such that the cross patterns of the substrate 105 overlap those of the shadow mask 102. Like this, to align the substrate 105 and the shadow mask 102, two CCD cameras 106 and two cross patterns for each of the substrate 105 and the shadow mask 102 are required.
As shown in FIG. 2, when the substrate 105 and the shadow mask 102 are exactly aligned, a chuck 107 goes down and fixes the substrate 105. A magnet 108 is disposed at a bottom of the chuck 107 and prevents the shadow mask 102 from hanging down. Accordingly, the shadow mask 102 including the ferromagnetic materials is easily fixed by the magnet 108 of the chuck 107. Then, a source (not shown) is evaporated and is deposited on the substrate 105 through the shadow mask 102 to form thin film patterns.
By the way, the shadow mask 102 may be magnetized depending on a magnetic field strength of the magnet 108, causing problems.
That is, the substrate 105 and the shadow mask 102 are fixed by the magnet 108 of the chuck 107, which is ferromagnetic, and then the thin film patterns are formed on the substrate 105. At this time, the shadow mask 102 may be magnetized. After that, the magnet 108 of the chuck 107 moves upward. Then, the shadow mask 102 may be demagnetized, and the magnetism of the shadow mask 102 may be removed.
However, the shadow mask 102 is still magnetized.
FIG. 3 shows a magnetized shadow mask of the related art. In FIG. 3, the shadow mask 102 may be a grill type. When the shadow mask 102 is fixed with the substrate 102 by the magnet 108 of FIG. 2, the shadow mask 102 may be magnetized. After forming the thin film patterns and removing the magnet 108, the shadow mask 102 is still magnetized, and thus adjacent grill patterns of the shadow mask 102 may be contacted to each other. Therefore, thin film patterns may be improperly formed due to the contacted grill patterns of the shadow mask 102 in a subsequent process. Defects may be caused in a display device.